# Flowchart Development

We know what a flowchart is and what purpose it serves (organizing our thinking about a process) from the early part of this course. Let's look at a few flowchart requirements and then some conventions:

### Requirements:

• Draw the process units and any streams connecting them
• Write the values and units of known stream variables
• Write each known stream flow and composition
• Assign algebraic symbols to unknown stream variables and put units on the unknowns!

There are three methods for conveying stream flows/compositions:

• Method 1: show a flow for each component
• Method 2: show a total flow, and fractional compositions of each component
• Method 3 (overkill): show a total flow and a flow for each component

### Conventions:

• typically use uppercase letters for total flows (or masses) and lowercase for component flows (or masses)
• moles are typically denoted with "n" and masses with "m"
• overdots denote rates
• fractions are denoted as "x"in the liquid phase and "y" in the gas phase, "z" for the total fraction (including *both* liquid and gas)

NOTE:

Flowcharts may be scaled.

It is not surprising that changing a flowchart from using units of lbm to kg should not make a difference to the validity of the flowchart. (unit conversions will not change whether the flowchart is balanced or not!)

With a little thinking then, it should be clear that changing the basis of calculation of a flowchart should not make a difference!

DEFINITION:

A basis of calculation is the one stream whose amount (mass or motes) or flow rate (mass flow or molar flow) is chosen as the "least common denominator" for the problem (the units that you match everything to, as well as the scale you match everything to!).

EXAMPLE:

For example: both of these expressions are true

60s + 120s = 180s
1 min + 2 min = 3 min

Changing the units did not effect the truth of the statement. It should be equally clear that scaling up (multiplying by a number greater than 1) or scaling down (multiplying by a number less than 1) also makes little difference.

60s + 120s = 180s
6s + 12s = 18s (multiply by 1/10)
120s + 240s = 360s (multiply by 2)

OUTCOME

Draw and label a flowchart from a process description.

TEST YOURSELF

Let's try and work through an example.